I've only called a foot fault in a leauge match once. It was a doubles match, we were down but I felt like we should have be able to handle these guys so I was irritated. One of the opponants was a pretty flagarant foot faulter (as are nearly 50% of players you see in usta leagues it seems). So during a changeover after one of his service games I said something like "by the way you may not know but you pretty much foot fault on every serve". He seemed in disbelief and looked at his partner who said "yeah actually you do". His next service game he of course foot faulted so I called it. After that I guess it got in his head, we broke him and it turned the match around and we won.

So there you go. positve impact from calling a foot faulter.

I think what was really positive is that his partner agreed! Gave the foot faulter little to argue about.